A headrest sliding device of the prior art has been suggested, for example, as disclosed in the Patent Literature 1 (Korea Registered Patent Publication No. 10-1144870) and the Patent Literature 2 (Korea Registered Patent Publication No. 10-1570427) that had been filed earlier by the applicant(s) of this application.
The mechanism of the headrest sliding device of the Patent Literature 1 is that if a headrest is to be returned to its original position from the locking state established after it is moved to a desired position by a user as shown in FIG. 1, the shaft unit 520 is pushed towards the direction of the rotating axis of the poles 600 and 700 so that the contact points thereof are shifted from the small-diameter shaft portion 522 to the large-diameter shaft portion 521 so as to lift up the poles 600 and 700, thereby releasing the locking.
That is, since the locking is released by a cam-like structure wherein the shaft unit 520 is being pushed and pulled along the direction of the rotating axis of the poles 600 and 700, there is an inconvenience in that since the shaft unit 520 must be slided along the right angle direction with respect to the pressing force of the poles 600 and 700, a large initial force must be applied for pressing.
In the headrest sliding device of the Patent Literature 2, as illustrated in FIG. 3, a lever member 10″ is rotatably supported at the second link 400 which is a movable part, and the pole 100″ is supported at the lower side link 300 which is a fixed part.
In this way, since the lever member 10″ is supported at the second link 400 which is a movable part, and the pole 100″ is supported at the lower side link 300 which is a fixed part, the point in the stopping protrusion 170′, where the pressing portion 13″ of the lever member 10″ should press, becomes different during the process of releasing the gearing between the pole and the ratchet, as illustrated in FIG. 4, therefore, the stopping protrusion 170′ of the pole 100″ is externally protruded long in length and affects the limited thickness of the headrest undesirably.